Helical stacked integrated inductor and transformer

ABSTRACT

A helical stacked integrated inductor formed by a first inducing unit and a second inducing unit includes a first helical coil and a second helical coil. The first helical coil is substantially located at a first plane and includes a first outer turn and a first inner turn. The first inner turn is surrounded by the first outer turn. The first helical coil forms a part of the first inducing unit and a part of the second inducing unit. The second helical coil is substantially located at a second plane different from the first plane and overlaps the first helical coil. The second helical coil forms a part of the first inducing unit and a part of the second inducing unit. The first helical coil and the second helical coil are stacked in a staggered arrangement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transformer and an inductor,especially to a helical stacked integrated transformer and a helicalstacked integrated inductor.

2. Description of Related Art

Inductors and transformers are important elements in radio frequencyintegrated circuits to implement single-ended to differential signalconversion, signal coupling and impedance matching. As System-on-chips(SoC) become the mainstream of integrated circuits, integrated inductorsand integrated transformers gradually substitute conventional discreteelements and are commonly applied to radio frequency integratedcircuits. However, inductors and transformers in integrated circuitsoften take up large areas; therefore, it becomes an important issue toreduce the areas of inductors and transformers in integrated circuitswithout degrading element performances, such as inductance, qualityfactor (Q), and coupling coefficient (K).

SUMMARY OF THE INVENTION

In view of the issues of the prior art, an object of the presentinvention is to provide a helical stacked integrated transformer and ahelical stacked integrated inductor in order to reduce component areasand enhance component performances, and further to improve symmetry ofthe components.

A helical stacked integrated transformer is disclosed. The helicalstacked integrated transformer is formed by a first inductor and asecond inductor and comprises a first helical coil and a second helicalcoil. The first helical coil is substantially located at a first planeand has a first outer turn and a first inner turn. The first inner turnis surrounded by the first outer turn, and the first helical coil formsa part of the first inductor and a part of the second inductor. Thesecond helical coil is substantially located at a second plane differentfrom the first plane, and shares an overlapped region with the firsthelical coil. The second helical coil forms a part of the first inductorand a part of the second inductor. At least one side of the first outerturn corresponds to a metal segment of the second helical coil along onedirection, and at least one side of the first inner turn does notcorrespond to the metal segment of the second helical coil along thedirection. The direction is a direction perpendicular to the first planeor the second plane.

A helical stacked integrated inductor is also disclosed. The helicalstacked integrated inductor is formed by a first inducing unit and asecond inducing unit and comprises a first helical coil and a secondhelical coil. The first helical coil is substantially located at a firstplane and has a first outer turn and a first inner turn. The first innerturn is surrounded by the first outer turn, and the first helical coilforms a part of the first inducing unit and a part of the secondinducing unit. The second helical coil is substantially located at asecond plane different from the first plane, and shares an overlappedregion with the first helical coil. The second helical coil forms a partof the first inducing unit and a part of the second inducing unit. Atleast one side of the first outer turn corresponds to a metal segment ofthe second helical coil along one direction, and at least one side ofthe first inner turn does not correspond to the metal segment of thesecond helical coil along the direction. The direction is a directionperpendicular to the first plane or the second plane.

The disclosed helical stacked integrated transformer and the helicalstacked integrated inductor have symmetric integrated structures,thereby providing two highly symmetric inductors or inducing units. Byarranging two helical coils in a staggered manner, the terminals of theintegrated transformer and the integrated inductor are located at theoutermost turn of the helical coil, which reduces winding complexity ofthe helical coil. In comparison to a conventional single-layeredintegrated inductor having the same inductance value and quality factor(Q), this invention greatly reduces component areas.

These and other objectives of the present invention no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiments withreference to the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a helical stacked integrated inductor according to anembodiment.

FIG. 2 illustrates a cross-sectional view of the helical stackedintegrated inductor 100.

FIG. 3 illustrates a helical stacked integrated inductor according toanother embodiment.

FIG. 4 illustrates a helical stacked integrated inductor according toanother embodiment.

FIG. 5 illustrates a cross-sectional view of the helical stackedintegrated inductor 400.

FIG. 6 illustrates a helical stacked integrated inductor according toanother embodiment.

FIGS. 7A-7C illustrates a helical stacked integrated inductor and itscross-sectional views according to another embodiment.

FIG. 8 illustrates a helical stacked integrated transformer according toan embodiment.

FIG. 9 illustrates a helical stacked integrated transformer according toanother embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following description is written by referring to terms of thistechnical field. If any term is defined in this specification, such termshould be explained accordingly. In addition, the connection betweenobjects or events in the below-described embodiments can be direct orindirect provided that these embodiments are practicable under suchconnection. Said “indirect” means that an intermediate object or aphysical space exists between the objects, or an intermediate event or atime interval exists between the events.

FIG. 1 illustrates a helical stacked integrated inductor according to anembodiment. The helical stacked integrated inductor 100 is made up of ahelical coil 110 and a helical coil 120. Most metal segments of thehelical coil 110 are located in a first metal layer of a semiconductorstructure, and most metal segments of the helical coil 120 are locatedin a second metal layer of the semiconductor structure. In other words,the helical coil 110 is substantially located at a plane where the firstmetal layer exists, and the helical coil 120 is substantially located ata plane where the second metal layer exists. The helical coil 110 has aterminal 111-a, a terminal 111-b, and metal segments 112, 113, 114 and131. Except the metal segment 131 that is located in a third metal layerdifferent from the first and second metal layers, the remaining metalsegments and all of the terminals are located in the first metal layer.The metal segment 131 connects the metal segment 113 and the metalsegment 114 through a via structure or a via array at the throughpositions 110-c and 110-d, respectively. The helical coil 120 has aterminal 121 and two metal segments 122 and 123. The terminal 121 andthe metal segments 122 and 123 are located in the second metal layer.

The helical stacked integrated inductor 100 includes two inducing units,which are the first inducing unit (represented by metal segments inlight grey) and the second inducing unit (represented by metal segmentsin dark grey). The current flowing into the first inducing unit throughthe terminal 111-b passes the metal segment 112, and flows to the metalsegment 122 through the via structure or the via array at the throughpositions 110-a and 120-a before flowing out through the terminal 121.Likewise, the current flowing into the second inducing unit through theterminal 111-a passes the metal segments 113, 131 and 114, and flows tothe metal segment 123 through the via structure or the via array at thethrough positions 110-b and 120-b before flowing out through theterminal 121. In fact, the terminal 121 is the center tap of the helicalstacked integrated inductor 100, and can be connected to a voltagesource or ground of an application circuit employing the helical stackedintegrated inductor 100. Obviously, the first inducing unit mainlyincludes a half of an outer turn of the helical coil 110 (i.e., the partof the metal segment 112 located at the outer turn), a half of an innerturn of the helical coil 110 (i.e., the part of the metal segment 112located at the inner turn), and a half of the helical coil 120 (i.e.,the metal segment 122). The second inducing unit mainly includes theother half of the outer turn of the helical coil 110 (i.e., the metalsegment 113), the other half of the inner turn of the helical coil 110(i.e., the metal segment 114), and the other half of the helical coil120 (i.e., the metal segment 123). In other words, most metal segmentsof the two inducing units of the helical stacked integrated inductor 100are evenly distributed in two metal layers, and thus the two inducingunits have excellent symmetry, hence providing the two inducing unitswith similar quality factors and inductance values. If, on the contrary,most metal segments of one of the two inducing units are located in thefirst metal layer while most metal segments of the other are located inthe second metal layer, the two inducing units may probably be moredistinct from each other in terms of quality factors and inductancevalues due to different characteristics (e.g., thickness, distance fromthe substrate, and the like) of the two metal layers.

In fact, the helical coil 110 and the helical coil 120 are stackedstructures. The part of the metal segment 112 at the outer turn isoverlapped without coming into contact with most part of the metalsegment 122, and the metal segment 113 is overlapped without coming intocontact with most part of the metal segment 123. FIG. 2 is across-sectional view of the helical stacked integrated inductor 100(depicted with respect to the cross section A-A′ in FIG. 1). In FIG. 2,the first metal layer (i.e., the metal layer where the helical coil 110exists) is under the second metal layer (i.e., the metal layer where thehelical coil 120 exists). For example, the first metal layer may be theUltra-Thick Metal (UTM) layer of a semiconductor process, and the secondmetal layer may be the redistribution layer (RDL) of the semiconductorprocess. The two layers can be exchanged in other embodiments. In otherembodiments, an under bump metallization (UBM) layer, stackedinter-metal layers, a second RDL, or other similar metal layers can alsobe used. As shown in FIG. 2, the helical coil 110 has one more turn thanthe helical coil 120. The outer turn of the helical coil 110 isoverlapped without coming into contact with the helical coil 120 along adirection perpendicular to the plane where the helical coil 110 or thehelical coil 120 exists (with an oxide layer in a semiconductorstructure sandwiched between the two helical coils, for example), andthe inner turn of the helical coil 110 does not correspond to any metalsegment of the helical coil 120 along the same perpendicular direction.With this staggered arrangement (i.e., the two helical coils of thehelical stacked integrated inductor 100 have different numbers of turns,and a part of the metal segments of the helical coil with more turns(the metal segment of the inner turn in this embodiment) does notcorrespond to the metal segments of the other helical coil), the helicalstacked integrated inductor 100 has an advantage, in addition to greatsymmetry, of being able to have its center tap (i.e., the terminal 121)arranged at an outer side of the helical coil; thus there is no need touse another metal layer other than the first and second metal layers toimplement the center tap.

The helical stacked integrated inductor of this invention is not limitedto a two-turn to one-turn combination as shown in FIG. 1. As shown inFIG. 3, the helical stacked integrated inductor 300 is made up ofhelical coils 310 and 320, which are respectively four-turn andthree-turn structures. Most metal segments of the helical coil 310 arelocated in the first metal layer, and most metal segments of the helicalcoil 320 are located in the second metal layer. Some of the metalsegments of the helical coil 310 are connected through a metal segmentin a third metal layer (the metal segments in the third metal layer arenot shown for the reason of clarity); for example, the metal segments312 and 314 are connected by a metal segment in the third metal layervia a pair of through structures 310-a and 310-b. Similarly, the throughstructures 310-c and 310-d are set as one pair, and the throughstructures 310-e and 310-f are set as one pair. Likewise, in the helicalcoil 320, the through structures 320-a and 320-b, which respectivelycorrespond to the through structures at two ends of the metal segment315 of the helical coil 310, are set as one pair, and the throughstructures 320-c and 320-d, which respectively correspond to the throughstructures at two ends of the metal segment 316 of the helical coil 310,are set as one pair. The first inducing unit (represented by metalsegments in light grey) has a first part located at the helical coil 310and a second part located at the helical coil 320, and the first andsecond parts are connected via corresponding through structures 310-gand 320-e. The second inducing unit (represented by metal segments indark grey) has a first part located at the helical coil 310 and a secondpart located at the helical coil 320, and the first and second parts areconnected via corresponding through structures 310-h and 320-f. As shownin FIG. 3, both the helical coil 310 and the helical coil 320 includemultiple turns. In each turn, about a half of the length of the metalsegment belongs to the first inducing unit and the other half belongs tothe second inducing unit, resulting in excellent symmetry of the helicalstacked integrated inductor 300. In addition, in spite of being formedin a structure with multiple turns, the helical stacked integratedinductor 300 can still have its center tap (i.e., the terminal 321)fabricated at the outermost turn of the helical coil 320 to diminishwinding complexity. In this embodiment, because there is one turndifference between the helical coils 310 and 320, when they are stacked,the metal segments at the innermost turn of the helical coil 310 doesnot correspond to any metal segment of the helical coil 320 along adirection perpendicular to a plane where the helical coil 310 or thehelical coil 320 exists.

In the embodiments of FIGS. 1 and 3, the input terminal and the centertap of the helical stacked integrated inductor are located at differentsides of the helical stacked integrated inductor; in another embodiment,they can be located at the same side of the helical stacked integratedinductor, as shown in FIG. 4. The helical stacked integrated inductor400 is made up of the helical coil 410 and the helical coil 420. Mostmetal segments of the helical coil 410 are located in the first metallayer of a semiconductor structure, and most metal segments of thehelical coil 420 are located in the second metal layer of thesemiconductor structure. The helical coil 410 has a terminal 411-a and aterminal 411-b, and further includes metal segments 412, 413, 414, 415,and 431. Except the metal segment 431 that is located in a third metallayer different from the first and second metal layers, the remainingmetal segments and all terminals are located in the second metal layer.The metal segment 431 connects the metal segment 412 and the metalsegment 413 through the via structure or via array at the throughpositions 410-a and 410-b, respectively. The helical coil 420 has aterminal 421, and further includes metal segments 422, 423 and 424. Theterminal 421 and the metal segments 422, 423, and 424 are located in thesecond metal layer.

The helical stacked integrated inductor 400 includes two inducing units,which are a first inducing unit (represented by metal segments in lightgrey) and a second inducing unit (represented by metal segments in darkgrey). The current flowing into the first inducing unit through theterminal 411-a passes the metal segments 412, 431 and 413, and flows tothe helical coil 420 through the via structure or the via array at thecorresponding through positions 410-d and 420-d. The through positions420-a and 420-b of the helical coil 420 respectively correspond to thethrough positions at two ends of the metal segment 415 of the helicalcoil 410. As a result, the current flowing into the helical coil 420flows through the metal segments 422 and 423 before flowing out throughthe center tap (i.e., the terminal 421) of the helical stackedintegrated inductor 400. Likewise, the current flowing into the secondinducing unit through the terminal 411-b passes the metal segment 414,and flows to the metal segment 424 of the helical coil 420 through thevia structure or the via array at the through positions 410-c and 420-cbefore flowing out through the terminal 421. Obviously, the firstinducing unit mainly includes a half of an outer turn of the helicalcoil 410 (i.e., the metal segment 412), a half of an inner turn of thehelical coil 410 (i.e., the metal segment 413), a half an outer turn ofthe helical coil 420 (i.e., the metal segment 423), and a half an innerturn of the helical coil 420 (i.e., the metal segment 422). The secondinducing unit mainly includes the other half of the outer turn of thehelical coil 410 (i.e., the part of the metal segment 414 at the outerturn), the other half of the inner turn of the helical coil 410 (i.e.,the part of the metal segment 414 at the inner turn), the other half ofthe outer turn of the helical coil 420 (i.e., the part of the metalsegment 424 at the outer turn), and the other half of the inner turn ofthe helical coil 420 (i.e., the part of the metal segment 424 at theinner turn). In other words, most metal segments of the two inducingunits of the helical stacked integrated inductor 400 are evenlydistributed in two metal layers, and thus the two inducing units haveexcellent symmetry, hence providing the two inducing units with similarquality factors and inductance values.

In fact, the helical coil 410 and the helical coil 420 are stackedstructures. The outer turn of the helical coil 410 is overlapped withoutcoming into contact with the inner turn of the helical coil 420. FIG. 5is a cross-sectional view of the helical stacked integrated inductor 400(depicted with respect to the cross section A-A′ in FIG. 4). In FIG. 5,the first metal layer (i.e., the metal layer where the helical coil 410exists) is under the second metal layer (i.e., the metal layer where thehelical coil 420 exists). The two layers can be exchanged in otherembodiments. As shown in FIG. 5, although the helical coil 410 and thehelical coil 420 are both two-turn structures, the coverage of thehelical coil 420 is greater than that of the helical coil 410. To bespecific, the outer turn of the helical coil 410 is overlapped withoutcoming into contact with the inner turn of the helical coil 420 along adirection perpendicular to a plane where the helical coil 410 or helicalcoil 420 exists, the inner turn of the helical coil 410 does notcorrespond to any metal segment of the helical coil 420 along the samedirection, and the outer turn of the helical coil 420 does notcorrespond to any metal segment of the helical coil 410 along the samedirection. With the staggered arrangement (i.e., the two helical coilsof the helical stacked integrated inductor 400 have the same number ofturns but different coverages, and the innermost turn of the helicalcoil with smaller coverage and the outermost turn of the helical coilwith greater coverage do not correspond to any metal segment of theother helical coil), the helical stacked integrated inductor 400 has anadvantage, in addition to great symmetry, of being able to have itscenter tap (i.e., the terminal 421) arranged at an outer side of thehelical coil. Therefore, there is no need to use another metal layerother than the first and second metal layers to implement the centertap.

The helical stacked integrated inductor of this invention is not limitedto the two-turn-and-two-turn combination shown in FIG. 4, and may be acombination of more turns. As shown in FIG. 6, the helical stackedintegrated inductor 600 is made up of helical coils 610 and 620, whichare respectively three-turn structures. Most metal segments of thehelical coil 610 are located in the first metal layer, and most metalsegments of the helical coil 620 are located in the second metal layer.Some of the metal segments of the helical coil 610 are connected througha third metal layer (the metal segments in the third metal layer are notshown for the reason of clarity); for example, the metal segments 612and 614 are connected by a metal segment in the third metal layer via apair of through structures 610-a and 610-b. Similarly, the throughstructures 610-c and 610-d are set as one pair. Likewise, in the helicalcoil 620, the through structures 620-a and 620-b, which respectivelycorrespond to the through structures at two ends of the metal segment615 of the helical coil 610, are set as one pair, and the throughstructures 620-c and 620-d, which respectively correspond to the throughstructures at two ends of the metal segment 616 of the helical coil 610,are set as one pair.

The first inducing unit (represented by metal segments in light grey)has a first part located at the helical coil 610 and a second partlocated at the helical coil 620, and the first and second parts areconnected via corresponding through structures 610-e and 620-e. Thesecond inducing unit (represented by metal segments in dark grey) has afirst part located at the helical coil 610 and a second part located atthe helical coil 620, and the first and second parts are connected viacorresponding through structures 610-f and 620-f. As shown in FIG. 6,both the helical coil 610 and the helical coil 620 include multipleturns. In each turn, about a half of the length of the metal segmentbelongs to the first inducing unit and the other half belongs to thesecond inducing unit, resulting in excellent symmetry of the helicalstacked integrated inductor 600. In addition, in spite of being formedin a structure with multiple turns, the helical stacked integratedinductor 600 can still have its center tap 621 fabricated at theoutermost turn of the helical coil 620 to diminish winding complexity.In this embodiment, the helical coils 610 and 620 have the same numberof turns; as a result, when they are stacked, the metal segments at theinnermost turn of the helical coil 610 and the metal segments at theoutermost turn of the helical coil 620 do not correspond to any metalsegment of the other helical coil along a direction perpendicular to aplane where the helical coil 610 or the helical coil 620 exists.

FIG. 7A illustrates the helical stacked integrated inductor according toanother embodiment. The helical stacked integrated inductor 700 issimilar to the helical stacked integrated inductor 400 as their inputterminal and center tap are both located at the same side of theinductor, except that in the helical coil 710 and the helical coil 720,the metal segments at the side where the input terminal (or the centertap) exists and its opposite side (i.e., the two sides parallel to thecross section A-A′) are staggered (i.e., the metal segments in the upperand lower layer are not correspondingly arranged), while the metalsegments at the other two sides (i.e. the two side parallel to the crosssection B-B′) are correspondingly arranged. Refer to the cross-sectionalviews in FIGS. 7B and 7C (corresponding respectively to cross sectionsA-A′ and B-B′) for better understanding of the staggered arrangement andthe corresponding arrangement mentioned above. In the cross-sectionalview in FIG. 7B, the metal segments at the inner turn and the outer turnof the helical coil 710 correspond respectively to the metal segments atthe inner turn and the outer turn of the helical coil 720 along thedirection perpendicular to a plane where the helical coil 710 or thehelical coil 720 exists. This arrangement in FIG. 7B is referred to asthe corresponding arrangement. In the cross-sectional view in FIG. 7C,the metal segments at the outer turn of the helical coil 710 correspondto the metal segments at the inner turn of the helical coil 720 alongthe direction perpendicular to a plane where the helical coil 710 orhelical coil 720 exists, but the metal segments at the inner turn of thehelical coil 710 and the metal segments at the outer turn of the helicalcoil 720 do not correspond to any metal segments of the other helicalcoil. This arrangement in FIG. 7C is referred to as the staggeredarrangement.

In addition to the helical stacked integrated inductor, a helicalstacked integrated transformer is also disclosed. FIG. 8 illustrates ahelical stacked integrated transformer according to an embodiment. Thestructure of the helical stacked integrated transformer in FIG. 8 issubstantially similar to that of the helical stacked integrated inductor100 in FIG. 1, except that the terminal 121 of the helical stackedintegrated inductor 100 is replaced by the terminals 821-a and 821-b inthe helical stacked integrated transformer 800. To be specific, thefirst inducing unit of the helical stacked integrated inductor 100 formsa first inductor in the helical stacked integrated transformer 800 (withthe terminals 811-a and 821-a serving as the two terminals of theinductor), and the second inducing unit of the helical stackedintegrated inductor 100 forms a second inductor in the helical stackedintegrated transformer 800 (with the terminals 811-b and 821-b servingas the two terminals of the inductor). The first inductor and the secondinductor together form a transformer with the terminals 811-a and 821-aserving as one port of the transformer and the terminals 811-b and 821-bserving as the other. In this embodiment, the terminals of the helicalcoil 810 and the terminals of the helical coil 820 are located atdifferent sides of the helical stacked integrated transformer 800.

FIG. 9 illustrates the helical stacked integrated transformer accordingto another embodiment. The structure of the helical stacked integratedtransformer is substantially similar to that of the helical stackedintegrated inductor 400 in FIG. 4, except that the terminal 421 of thehelical stacked integrated inductor 400 is replaced by the terminals921-a and 921-b in the helical stacked integrated transformer 900. Theterminals 911-a and 921-a form the two terminals of the first inductor,and the terminals 911-b and 921-b form the two terminals of the secondinductor. In this embodiment, the terminal of the helical coil 910 andthe terminal of the helical coil 920 are located at the same side of thehelical stacked integrated transformer 900. Similarly, by modifying thecenter taps of the helical stacked integrated inductors 300 and 600 inFIGS. 3 and 6 to two terminals, corresponding helical stacked integratedtransformers can be generated.

Note that the shape, size, ratio of any element, and the number of turnsof the helical coils in the disclosed figures are exemplary forunderstanding, not for limiting the scope of this invention. In theaforementioned embodiments the helical coils are made as rectangles, butthey can also be made as other polygons. Moreover, the width of themetal segment at each turn of the helical coil may differ from oneanother; for example, the width of the metal segment at the inner turncan be designed to be greater than the width of the metal segment at theouter turn. The quality factor (Q) of the inductor decreases as theradius of the coil becomes smaller. However, by increasing the width ofthe metal segment at the inner turn, the quality factor (Q) can beimproved, which demonstrates a more significant effect than increasingthe width of the metal segment at the outer turn.

The aforementioned descriptions represent merely the preferredembodiments of the present invention, without any intention to limit thescope of the present invention thereto. Various equivalent changes,alterations, or modifications based on the claims of the presentinvention are all consequently viewed as being embraced by the scope ofthe present invention.

What is claimed is:
 1. A helical stacked integrated transformer, formedby a first inductor and a second inductor, comprising: a first helicalcoil, substantially located at a first plane and having a first outerturn and a first inner turn, wherein said first inner turn is surroundedby said first outer turn, said first inner turn and said first outerturn are connected through a connecting metal segment, and said firsthelical coil forms a part of said first inductor and a part of saidsecond inductor; and a second helical coil, substantially located at asecond plane different from said first plane, and sharing an overlappedregion with said first helical coil, wherein said second helical coilforms a part of said first inductor and a part of said second inductor;wherein, at least one side of said first outer turn corresponds to ametal segment of said second helical coil along one direction, and atleast one side of said first inner turn does not correspond to saidmetal segment of said second helical coil along said direction, saiddirection is a direction perpendicular to said first plane or saidsecond plane, wherein said helical stacked integrated transformer has afirst terminal and a second terminal, and said first terminal and saidsecond terminal are in a line symmetry with respect to a line passingthe connecting metal segment.
 2. The helical stacked integratedtransformer of claim 1, wherein said helical stacked integratedtransformer has a first terminal, a second terminal, a third terminal,and a fourth terminal, said first terminal and said second terminal arelocated at said first plane and at a first side of said helical stackedintegrated transformer, said third terminal and said fourth terminal arelocated at said second plane and at a second side of said helicalstacked integrated transformer, said first side is different from saidsecond side, and there is one turn difference between said first helicalcoil and said second helical coil.
 3. The helical stacked integratedtransformer of claim 2, wherein said second helical coil has a secondouter turn and a second inner turn, said second inner turn is surroundedby said second outer turn, said first terminal and said second terminalare located at said first outer turn, and said third terminal and saidfourth terminal are located at said second outer turn.
 4. The helicalstacked integrated transformer of claim 2, wherein said first terminaland said third terminal are two terminals of said first inductor, andsaid second terminal and said fourth terminal are two terminals of saidsecond inductor.
 5. The helical stacked integrated transformer of claim1, wherein said helical stacked integrated transformer has a firstterminal, a second terminal, a third terminal, and a fourth terminal,said first terminal and said second terminal are located at said firstplane and at a first side of said helical stacked integratedtransformer, and said third terminal and said fourth terminal arelocated at said second plane and at said first side of said helicalstacked integrated transformer, and said first helical coil and saidsecond helical coil have the same number of turns.
 6. The helicalstacked integrated transformer of claim 5, wherein said second helicalcoil has a second outer turn and a second inner turn, said second innerturn is surrounded by said second outer turn, said first terminal andsaid second terminal are located at said first outer turn, and saidthird terminal and said fourth terminal are located at said second outerturn.
 7. The helical stacked integrated transformer of claim 5, whereinsaid first terminal and said third terminal are two terminals of saidfirst inductor, and said second terminal and said fourth terminal aretwo terminals of said second inductor.
 8. A helical stacked integratedinductor, formed by a first inducing unit and a second inducing unit,comprising: a first helical coil, substantially located at a first planeand having a first outer turn and a first inner turn, wherein said firstinner turn is surrounded by said first outer turn, said first inner turnand said first outer turn are connected through a connecting metalsegment located at a second plane different from said first plane, andsaid first helical coil forms a part of said first inducing unit and apart of said second inducing unit; and a second helical coil,substantially located at a third plane different from said first planeand said second plane, and sharing an overlapped region with said firsthelical coil, wherein said second helical coil forms a part of saidfirst inducing unit and a part of said second inducing unit; wherein, atleast one side of said first outer turn corresponds to a metal segmentof said second helical coil along one direction, and at least one sideof said first inner turn does not correspond to said metal segment ofsaid second helical coil along said direction, said direction is adirection perpendicular to said first plane or said third plane; whereinsaid helical stacked integrated inductor has a first terminal and asecond terminal, and said first terminal and said second terminal are ina line symmetry with respect to a line passing the connecting metalsegment.
 9. The helical stacked integrated inductor of claim 8, whereinsaid helical stacked integrated inductor further has a third terminal,said first terminal and said second terminal are located at said firstplane and at a first side of said helical stacked integrated inductor,said third terminal is located at said third plane and at a second sideof said helical stacked integrated inductor, said first side isdifferent from said second side, and there is one turn differencebetween said first helical coil and said second helical coil.
 10. Thehelical stacked integrated inductor of claim 9, wherein said secondhelical coil has a second outer turn and a second inner turn, saidsecond inner turn is surrounded by said second outer turn, said firstterminal and said second terminal are located at said first outer turn,and said third terminal is located at said second outer turn.
 11. Thehelical stacked integrated inductor of claim 9, wherein said firstterminal and said third terminal are two terminals of said firstinducing unit, and said second terminal and said third terminal are twoterminals of said second inducing unit.
 12. The helical stackedintegrated inductor of claim 8, wherein said helical stacked integratedinductor has a first terminal, a second terminal and a third terminal,said first terminal and said second terminal are located at said firstplane and at a first side of said first helical coil, said thirdterminal is located at said second plane and at said first side of saidsecond helical coil, and said first helical coil and said second helicalcoil have the same number of turns.
 13. The helical stacked integratedinductor of claim 12, wherein said second helical coil has a secondouter turn and a second inner turn, said second inner turn is surroundedby said second outer turn, said first terminal and said second terminalare located at said first outer turn, and said third terminal is locatedat said second outer turn.
 14. The helical stacked integrated inductorof claim 12, wherein said first terminal and said third terminal are twoterminals of said first inducing unit, and said second terminal and saidthird terminal are two terminals of said second inducing unit.